Bimetallic spring support for a shadow mask

ABSTRACT

In order to check displacement of a shadow mask in a plane at right-angles to the axis of a cathode-ray tube, it is suspended from three flat springs consisting of two strips which are welded together along their narrow sides and constitute a bimetal; the coefficient of expansion of said springs is adapted to the location of the springs on the shadow mask edge by the location of the supporting point of the spring to the envelope, on a line at right-angles to the welding seam at different distances from the welding seam.

O United States Patent [111 3,617,787

[72] Inventor Gerardus Wilhelmus Plukker [56] A Relerences Cited m w Emmaslngel, Eindhoven, Netherlands UNITED STATES PATENTS [21] Appl. No. 834,684

2,795,718 6/1957 Van Hekken et a1. 313/85 [22] Filed June 19, 1969 3,454,813 7/1969 Lewmson 313/85 X [45] Pmmed 1971 3 449 611 6/1969 s 11 tz t 1 313/85 [32] Pdority June 21 1968 c war e a [33] Netherlands Primary Examiner-Roy Lake [3 1 6808720 Assistant Examiner-V. Lafranchi 7 MM. 7, V WM V. H Anomey-Frank R. Trifari [54] r ig SPRING SUPPORT FOR A SHADOW ABSTRACT: In order to check displacement of a shadow 3 Chimsfi Drawing Filth mask ina plane at right-angles to the axis of a cathode-ray tube, 1t is suspended from three flat springs consisting of two [52] US. Cl 313/85, tri whi h are welded together along their narrow sides and 313/2 2, 29/195.5, 29/196-6 constitute a bimetal; the coefficient of expansion of said [51] Int. Cl "H0lj 29/46, springs i ada ted t the location of the springs on the shadow 1 31/20 mask edge by the location of the supporting point of the spring [50] Field of Search 313/85 S, to the envelo e, on a line at right-angles to the welding seam at different distances from the welding seam.

PATENTEDHEWZ Ian 3,617,787

GERARDUS W. PLUKKER BIMETALLIC SPRING SUPPORT FOR A SHADOW MASK The invention relates to a color television picture tube comprising a window having an upright edge, a cone and a neck and in which near the luminescent screen a substantially rectangular color selection electrode, for example, a shadow mask, is provided, which electrode is supported by the upright edge of the window by means of at least three strip-shaped springs placed along the straight sides of the color selection electrode, the color selection electrode, upon being heated, being moved towards the screen by means of bimetallic components, so that the electron beams always impinge upon the correct phosphor dots.

According to an embodiment described in application Ser. No. 795,969, filed Feb. 3, 1969, said movement towards the screen is obtained by means of flat springs arranged along the straight sides and each consisting of two strips which are welded together with their narrow sides and extend in the length of the spring and together constitutes a bimetal. These strips are arranged substantially parallel to the edge of the associated straight sides of the color selection electrode and welded to said electrode with one end, the other free end being supported by the upright edge of the window by means of a supporting point.

Dependent upon the length of the coefficient of expansion of the springs, the coefficient of expansion of the material of the color selection electrode, and the location where the springs are provided along the perimeter of said electrode, the color selection electrode, upon being heated, will experience a displacement in a plane at right-angles to the tube axis. This may be both a displacement in the lateral direction and a rotation of the axes of said electrodes extending at right-angles to the straight sides. In order to avoid such a displacement, the expansion of each spring will hence have to be equal to that of the part of the color selection electrode situated between the connection point of the spring to said electrode and the center of the side extending according to the longitudinal axis of said spring. The coefficient of expansion of a spring of a given length hence is dependent upon the location where the said spring is secured to a straight side. So it would be necessary to use springs of different materials for the various suspension points. However, this is not possible in the production, so that a compromise always had to be concluded. Dependent upon the location of the spring with respect to the center of the straight side, the expansion must be directed opposite to or equal to that of the said part of the electrode.

The said drawback can be avoided entirely if, according to the invention, each flat spring consists of two strips which are secured together with one narrow side and which extend along the longitudinal axis. Each strip consists of one of the metals constituting together a bimetal. One end of the spring is secured to the color selection electrode and the other free end is supported by the upright edge of the window by means of a supporting point. This supporting point is situated, dependent upon the location and the position of the spring with respect to the center of the associated straight side of the color selection electrode, on a line at right-angles to the welding seam at such a distance from said welding seam that the expansion of the free part of the spring between the connection point and the supporting point is substantially equal to the expansion of the part of the color selection electrode situated between the connection point of the spring and the center of the straight side of the color selection electrode associated with said spring.

When the supporting point is situated in the bimetallic part which has the greatest coefficient of expansion, the displacement of the electrode, as a result of the variation in length of the free part of the spring, will be larger than when the supporting point is situated on the strip having the smallest coefficient of expansion. According to the invention, the coefficient of expansion of the spring is adapted to the expansion of the part of the straight side of the color selection electrode situated between the connection point of the spring and the center of said side.

The invention will now be described with reference to the accompanying drawing, in which:

FIGS. 1 and 2 diagrammatically show a color selection electrode in the form of a shadow mask.

FIGS. 3 and 4 are elevations of a bimetallic spring according to the invention, and

FIG. 5 is a plan view ofFIG. 4, while FIG. 6 is a perspective view of a mounted bimetallic spring shown in FIG. 3.

FIG. 7 is a side view of the front section of a color-television tube showing the fluorescent screen, shadow mask and bimetallic springs.

In FIG. 1, reference numeral 1 denotes the perimeter of a shadow mask which is suspended, by means of bimetallic springs 2, 3 and 4 and supporting points 5, in an upright edge of a window 21 provided with a fluorescent screen 22 of a color television picture tube. The springs are welded to the mask at 6.

If upon expansion of the mask 1 by heating the center M of the mask must remain in its place, the overall expansion of. the spring 2 will have to be equal to the expansion of the part 7 of the mask 1, because the supporting point 5 of said spring lies just opposite to the center of the associated straight side of the mask. So the spring 2 must have the same coefficient of expansion as the mask 1. The spring 3 must have no expansion for the center of the associated straight side of the mask I to which the spring is secured to remain in its place, since the expansion of the mask from said center upwards and downwards is equal and the connection point 6 of spring 3 and the mask 1 lies just on a center line through said center M. In order that this point may not be displaced by expansion of the spring 3 with respect to the supporting point 5 of said spring the coefficient of expansion of the spring 3 must be zero. In the arrangement of spring 4 it is necessary that the expansion of the part 8 of the mask is equal to that of the spring 4. In this case the part 8 is approximately twice as long as the length of the spring 4,

so that the coefficient of expansion of the spring 4 in this arrangement must be approximately two times as large as that of the material of the mask 1.

Therefore, it must be possible to adapt the coefficient of expansion of the material of the springs to the arrangement thereof with respect to the center of the associated straight side of the mask, if all the springs have the same length, which is desirable for structural reasons. Consequently, it would be necessary for all the springs to either consist of different materials or to have different lengths. For practical purposes this has great drawbacks, the more so because the springs are of a bimetal as is shown in FIGS. 3 and 4. The object hereof is to move the mask, upon expansion, towards the luminescent screen, so as to keep the holes on the connection line of the connection point and the associated phosphor dot. A simplification is provided by the arrangement shown in FIG. 2, in which the springs 3 and 9 can be equal.

The spring 2 shown in FIG. 3 consists of a part 6 which is welded to the edge of the mask and the strip I2 of which is bent around the edge along the line 15 to obtain a larger rigidity of the connection as is shown in FIG. 6. The spring 2 consists of a strip 10 extending in a direction toward the screen and consisting of chromium-nickel steel having 18 percent by weight of chromium and 8 percent by weight of nickel and a coefficient of expansion of 17x10, and a strip 11 consisting of Invar (36 percent by weight of Ni, 64 percent by weight of Fe) having a coefficient of expansion of 1X10.

The expansion of the spring is determined by the free length 20. When the supporting point 13 is situated at A on the extreme edge of the strip 10, (FIG. 4) a coefficient of expansion will hold for the spring of AD=17XIO. When the supporting point 13 is in point B of the strip 11, a coefficient of expansion of the spring of 1X10 will apply. In FIG. 3 the supporting point 13 is situated on the welding seam 14 of the strips 10 and 11, so that an intermediate coefficient of expansion is obtained (FG in FIG. 4). Since the coefficient of expansion of the material of the mask which consists of soft steel is approximately 12x10, the spring 2 shown in FIG. 3 will hence have approximately the same coefficient of expansion as the mask 1, which is required.

For springs 3 and 9, which must have a coefficient of expansion which is as small as possible, the supporting point 13 is situated entirely on the extreme edge of the strip 17 which consists of lnvar. For that purpose, the strip 17 comprises a lug 18, since actually the supporting point always has a given dimension. By increasing the distance of the supporting point 13 on the strip 17 with respect to the welding seam, for example, by providing said supporting point 13 in the lug 18, the effect of the coefficient of expansion can be intensified. If, for example, the lug 18, in which the supporting point 13 is situated (FIG. 4), is elongated so that the supporting point 13 becomes located farther from the welding seam 19, even the effect of a shortening of the spring length can be obtained (EC in FIG. 4). 1f the supporting point would be provided on such a lug (not shown) of the chromium-nickel steel strip 16, an extra large coefficient of expansion could be obtained.

The invention consequently permits obtaining a movement of the mask towards the screen by the bimetal effect and also of obtaining the correct coefficient of expansion by the location of the aperture for the supporting point of the strip, so that the screen does not move in a direction at right-angles to the axis of the tube, notwithstanding the three-point suspen- Sln.

Although one example has been described, the invention can be applied not only to other color selection electrodes, for example, in the form of a wire grid for afterdeflection focusing, which grid is provided close in front of the luminescent screen, but also in all those cases in which the coefficient of expansion of a given strip must be adaptable to that of several other components. It is alternatively possible to use more than three springs.

What is claimed is:

l. A cathode ray tube comprising an evacuated envelope having a longitudinal axis and a substantially rectangular window portion at one end thereof intersecting said axis at rightangles, a plurality of phosphor triads constituting a luminescent screen disposed on said window, a substantially rectangular shadow mask having apertures therein aligned with said phosphor triads, and at least three strip-shaped flat springs positioned along the sides of the mask for supporting said shadow mask, each of said springs comprising two strips each of a different metal and each having a given longitudinal axis, said strips being joined along an edge extending in a direction parallel to the longitudinal axis of each strip, one end of said spring being secured to said mask and the other end being supported by an upright edge of the window by means of a support with the flat sides of said strips being parallel to the upright sides of the mask, said support being positioned on a line at right-angles to the joined edge at a distance therefrom at which the expansion of a free portion of the spring between the end of the spring secured to the mask and said support is substantially equal to the expansion of a portion of the mask located between the end of the spring secured to the mask and the center of the side of the mask whereby upon heating, substantially no displacement of the mask occurs in a plane at right-angles to the longitudinal axis of the tube.

2. A color television picture tube as claimed in claim 1, wherein a supporting spring is secured to a side of the mask in such manner that said support is situated opposite to the center of said side and on the joined edge of the bimetallic strip of the supporting spring, two other supporting springs being secured symmetrically with respect to the axis extending through said center and each being in the center of one of the sides extending parallel to said axis, the free ends pointing in the direction of the fourth straight side and said support of the said springs being situated each on the extreme edge of the part having the smallest coefficient of thermal expansion of the associated bimetallic spring.

3. A color television picture tube as claimed in claim 2 wherein said support is a lug provided at the free end of the flat supporting spring.

* i i i 7223; UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 787 Dated November 2, 1971 Invented/s4 GERARDUS WILHELMUS PLUKKER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 3, after "strip-shaped" insert --substantially--.

Signed and sealed this 6th day of February 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOT'I'SCHALK Commissioner of Patents Attesting Officer 

1. A cathode ray tube comprising an evacuated envelope having a longitudinal axis and a substantially rectangular window portion at one end thereof intersecting said axis at right-angles, a plurality of phosphor triads constituting a luminescent screen disposed on said window, a substantIally rectangular shadow mask having apertures therein aligned with said phosphor triads, and at least three strip-shaped flat springs positioned along the sides of the mask for supporting said shadow mask, each of said springs comprising two strips each of a different metal and each having a given longitudinal axis, said strips being joined along an edge extending in a direction parallel to the longitudinal axis of each strip, one end of said spring being secured to said mask and the other end being supported by an upright edge of the window by means of a support with the flat sides of said strips being parallel to the upright sides of the mask, said support being positioned on a line at right-angles to the joined edge at a distance therefrom at which the expansion of a free portion of the spring between the end of the spring secured to the mask and said support is substantially equal to the expansion of a portion of the mask located between the end of the spring secured to the mask and the center of the side of the mask whereby upon heating, substantially no displacement of the mask occurs in a plane at right-angles to the longitudinal axis of the tube.
 2. A color television picture tube as claimed in claim 1, wherein a supporting spring is secured to a side of the mask in such manner that said support is situated opposite to the center of said side and on the joined edge of the bimetallic strip of the supporting spring, two other supporting springs being secured symmetrically with respect to the axis extending through said center and each being in the center of one of the sides extending parallel to said axis, the free ends pointing in the direction of the fourth straight side and said support of the said springs being situated each on the extreme edge of the part having the smallest coefficient of thermal expansion of the associated bimetallic spring.
 3. A color television picture tube as claimed in claim 2 wherein said support is a lug provided at the free end of the flat supporting spring. 